Matrix isolation studies vibrational spectra

The bond distance and angle are from the electronic absorption spectrum as summarized by Herzberg ( ). The vibrational frequencies are obtained from Herzberg (1J[) and from matrix-isolation studies of Milligan and Jacox (15). 

The electronic levels and vibrational frequencies are those reported by Weltner and McLeod (7). The results were based on a matrix isolation study of Ta02 trapped in argon and neon matrices at 20 K and 4 K, respectively. The infrared spectrum was interpreted to favor a bent molecule in the ground state. Kaufman et al. (8) reported that TaO (g) is bent based on the... 

Not until 1985, did Owrutsky et al. [1, 4] have any success in the experimental determination of bond length and stretching fundamental, viz. 96.43 pm and 3555.6 cm- respectively, by measuring the vibration-rotation spectrum of free OH- ions. The corresponding data of OD- ions were reported by Rehfuss et al. [8] (96.42 pm and 2625.3 cm-1). These values were confirmed slightly later by matrix isolation studies, viz. 3554.0 and 2622.5 cm-1 for OH- and OD- in... 

The vibrational spectrum of TeF4 has been studied extensively, including matrix-isolation techniques (2). The most dilute matrices reveal absorptions attributable only to the monomeric TeF4 molecule, with C2v symmetry. The more concentrated matrices contain absorptions arising from several dimeric or oligomeric species (2). 

It is always desirable to back up IR absorption spectroscopy with Raman measurements. The different selection rules for the two techniques means that, at least for symmetric species, it is often necessary to have data from both types of measurement to have a full picture of the vibrational spectrum. Raman spectroscopy has been used to study many matrix-isolated species although there are problems regarding intensity and photosensitivity. An excellent review exists on the subject that highlights both the applications and difficulties of the method. A molecule that has been well characterized by both IR and Raman spectroscopy is the matrix-isolated species Mo(C )s(N2) (15). Spectra for (15) are illustrated... 

McDowell and coworkers (15J studied the high resolution infrared spectrum of UF5 at ambient and low temperatures. This work was followed by a series of vibrational and electronic spectroscopic studies of matrix isolated UFg (16,17,18,19,20). In the first experiments, UFg deposited in Ar or CO matrices was vibrationally characterized by infrared spectroscopy and then exposed to broadband UV radiation at 10°K. In argon, photoreduction proceeded rapidly the 619 cirri UF5 infrared peak decreased in intensity while two new peaks grew in at 584 cirri anc 561 cirri. The new peaks were assigned to the expected UF5 photolysis product and a tentative C4V structure assignment was made. The wavelength dependence of the photoreduction was studied using a monochroma-tized UV source (1 kw Hg-Xe lamp, Schoeffel 6M-250 monochromator). The relative quantum efficiency of the UF5 dissociation per unit absorbance of UFg was found to be relatively constant in the allowed B-X absorption band (250-300 nm) (T7). Radiation in the... 

Later, the experimental evidence for square cyclobutadiene was called into question. Krantz reported the photolysis of bicyclopyranone in which the carbon atom eliminated as CO2 was labeled with C. One important infrared band that had been assigned to a vibration of square planar cyclobutadiene in earlier studies was altered by the isotopic change, suggesting that this band was due to CO2 trapped with the cyclobutadiene in the rigid rare gas matrix. Thus, the experimental data did not answer the question of the structure of cyclobutadiene. Later work on the theoretical determination of the infrared spectrum of cyclobutadiene ° and further matrix isolation spectroscopy experiments, including the use of polarized IR spectroscopy... 

In the IR spectrum of the gas at 60 to 400Torr, the rotational subbands of the three fundamental vibrations and of the overtone 2v2(see p. 150) of HOF and DOF we re observed [7]. The spectrum of matrix-isolated HOF was studied at HOF N2 ratios of -1 3000 and -1 20000. The fundamental vibrations (see p. 149) were observed as well as a small band at 1393 cm definite only in the more concentrated matrix and presumably due to the bending mode of an HOF molecule hydrogen-bonded to HF, a product of thermal decomposition of HOF [8]. The complex spectra in N2 and Ar matrices are also partly due to HF HOF [9]. IR spectra of solid films were studied at -195°C, and the intramolecular vibrations v, V2, V3, 2v2, and 2v3 of HOF, DOF, and H OF were found. Bands at 628 and 448 cm" for HOF were ascribed to a simple cyclic dimer. But infinite planar zigzag chains could not be ruled out [10], and this latter interpretation is supported by the Raman spectrum (see table p. 154). 

The Stable carbonyl and thiocarbonyl halide molecules have been studied by IR as well as Raman spectroscopy. Normal coordinate analyses based on force constants transferred from other molecules (Urey-Bradley type), or from ab initio calculations, have aided in the vibrational assignments. Some of the unstable molecules which have been observed in the microwave have been characterized by infrared spectroscopy. The somewhat lower sensitivity of this method means that long path lengths of the gas may be needed. The identification of the various stable and unstable species in the microwave spectrum is simplified by the fact that the absorption lines are usually well resolved from each other. The widths of the bands in the infrared may make the transient species difficult to detect against the stronger absorptions of the stable side products. IR and Raman spectroscopies do have the advantage that they can be used on solid and liquid samples. Since the bands in a low temperature rare gas matrix have a narrower profile, the infrared spectrum is usually simplified over the room temperature gas phase spectrum. Moreover, the vibrational frequencies are only mildly perturbed by solid state effects. For example, CF Se has not been observed in the vapor phase, yet its vibrational dynamics are known from its matrix isolation spectrum. Table 9 gives the vibrational data for the carbonyl, thiocarbonyl, seleno-carbonyl and formyl halides. 

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